In precision work for which electric discharge machining is particularly suitable, it is important that the workpiece into which a predetermined structure has to be cut is held firmly against the bed of the vise. There is a tendency for the workpiece to move upwardly a slight amount from the bed when tightening the jaws of the vise. Such uncontrolled movement of the workpiece during tightening of the jaws prevents meeting close tolerances which are inherent in precision working.
Known wire cut electric discharge machines typically offer only a limited working range within which the workpiece has to be adjusted and held by the vise. Such working range is limited by the feeding means of the wire and the removing means of the wire between which the electric wire runs during wire cutting operation on the workpiece. It is therefore important that the vise for holding the workpiece within the working range occupies as little space as possible.
In U.S. Pat. No. 4,411,415 a compound jaw plate for a vise is disclosed wherein a jaw attaching plate and a workpiece engaging plate are connected by two pivotable links surrounded by an elastomeric material. The jaw attaching plate is adopted to be mounted to a jaw of the vise, and the workpiece engaging plate grips the workpiece to be held by the vise. The links are positioned at downward acute angles relative to the intended direction of applied force for gripping a workpiece. This device exerts a force on a gripped workpiece urging it towards the bed of the vise.
This known vise is intended for use in a milling cutter or the like, and therefore, has a very bulky construction. Moreover, an adjustment of a workpiece clamped inbetween the jaws of said vise cannot meet the very high requirements as to the accuracy of adjustment which has to be maintained throughout the complete electroerosive cutting operation on the workpiece. Typically, the workpiece has to be adjusted in the vise with an accuracy in the range of microns. Such adjustment cannot be obtained by the known vise because the pivotable mounting of the links to the workpiece gripping plate and to the jaw attaching plate of the jaw inherently gives cause to deviations in adjustment of the workpiece which exceed beyond the desired range of tolerance.